Recently, oncogenic RNA viruses have been shown to contain enzymes which catalyze the synthesis of DNA and hydrolyte RNA in a DNA-RNA hybrid. It is of interest to explore the role of these enzymes in the neoplastic process of the host cells. It is logical to look in the host nuclei for changes in and/or new enzymes which synthesize RNA and/or degrade RNA. DNA-dependent RNA polymerases have been solubilized and purified on DEAE-Sephadex resin from both normal and Friend virus (FV) infected mouse spleen as well as a variety of other cells. The DNA- dependent RNA polymerases have been separated from both DNAases as well as RNAases A and RNAase H. Additionally, the polymerases have been separated from the bulk of the highly positively changed proteins. The comparative profiles do reveal some distinct differences both quantitatively and qualitatively. The meanings of these changes are under current investigation. Studies are also being conducted on the elevation of RNAase H in the FV-infected tissue.